On 10/19/20 6:51 AM, Bodo Stroesser wrote: > This is made on top of the scsi-staging tree plus my previous > patch: > "scsi: target: tcmu: add compat mode for 32bit userspace on 64bit kernel" > > --- > > scatter_data_area and gather_data_area are not easy to understand, > since data is copied in nested loops over sg_list and tcmu dbi > list. Since sg list can contain only partly filled pages, the loop > has to be prepared to handle sg pages not matching dbi pages > 1 by 1. > > Existing implementation uses kmap_atomic()/kunmap_atomic() due to > performance reasons. But instead of using these calls strictly > nested for sg and dpi pages, the code holds the mappings in an > overlapping way, which indeed is a bug that would trigger on archs > using highmem. > > The scatterlist lib contains the sg_miter_start/_next/_stop > functions which can be used to simplify such complicated loops. > > The new code now processes the dbi list in the outer loop, while > sg list is handled by the inner one. That way the code can take > advantage of the sg_miter_* family calls. > > Calling sg_miter_stop() after the end of the inner loop enforces > strict nesting of atomic kmaps. > > Since the nested loops in scatter_/gather_data_area were very > similar, I replaced them by the new helper function > tcmu_copy_data(). > > Signed-off-by: Bodo Stroesser <bostroesser@xxxxxxxxx> > Acked-by: Mike Christie <michael.christie@xxxxxxxxxx>
